The agency confirmed that a number of searches had been conducted in Manchester involving a £30 million property portfolio that had been acquired over a period of time.
The searches were carried out on domestic and business properties linked with two Manchester-based businessmen.
The agency is believed to have been investigating the assets of alleged IRA chief-of-staff Thomas "Slab" Murphy.
A statement said: "The agency has so far identified approximately 250 properties held by both persons and a number of property management companies," it said.
"The equity in the properties appears to be in the region of £9 million."
The move by the agency followed a successful application to the High Court inLondon for search and seizure warrants and a disclosure order.
The agency's statement said during the searches large amounts of documentation were seized by their investigators.
"The agency has also served disclosure notices permitting compulsory questioning by financial investigators and a handover of legal and other documentation," the ARA confirmed.
"At this stage no further comment can be made on this case."
It is understood that Mr Murphy, a South Armagh farmer, has been underinvestigation by the Irish Republic's Criminal Assets Bureau.
He came to prominence in 1998 after he sued the Sunday Times newspaper unsuccessfully in an 11-year legal battle over claims that he was involved in IRA bombing campaigns in Britain.
He has a farm at Hackballscross, which straddles the border between Northern Ireland and the Irish Republic.
It is understood the properties under investigation include flats, a house and a large site in Stretford and a house in Sale.
One property believed to be linked to the investigation was raided this morningon Britannia Road in Sale, south Manchester.
The offices of Dermot Craven Developments Ltd and the Craven Group property companies were visited by police in riot gear at 8am, according to witnesses.
The modest two-storey office building is the headquarters of Craven Group, a well-known local firm in South Manchester.
The firm also has a letting shop in Sale and the business includes property sales, refurbishments and investment.
Builder Peter Barrie was working on a site across the road from the offices and saw police arrive.
He said: "An unmarked police car came down the road first and officers in blue riot uniforms got out.
"They sort of looked around and surrounded the area. As they got out, a couple more police vans came down the road with more officers.
"I would say there was about 25 to 30 in riot gear.
"The first lot pressed the buzzer on the office door, someone answered and two officers went inside. I haven't seen them take anything away yet.
"There is always a guy who drives a red Ferrari speeding up and down the road and going in there.
"There are always Porsches and other big motors in the car park.
"There's a lot of big Irish lads go in there. About three days ago I heard them singing some Irish songs, I think it was Gaelic, a big group of them, they were all merry."
Zohaib Qaiser, 21, a student who lives across the road, added: "There are always big cars parked outside. I just got the impression they were rich people.
"Cars would arrive at all times, even very late at night."
Two uniformed police officers stood guarding the entrance to the offices while more police were believed to be inside carrying out a search.
Police were also believed to be at another property in the wealthy village of Bowdon, Cheshire.
- More about: